Brother Facsimile Equipment MFC7420 - Manual (Page 211)

Confidential 9-23
M-5 Insufficient output from high-voltage power supply unit
Possible cause Step Check Result Remedy
High-voltage
contact 1 Do any of the terminals on
the high-voltage contacts
have dirt or contact burns? Yes Clean the terminals.
Yes Replace the high-voltage power
supply PCB.
High-voltage
power supply
PCB 2 Check the connections of
the connector between the
high-voltage power supply
and the main PCB are
secured correctly?
No Reconnect the connector
between the high-voltage power
supply and the main PCB.
M-6 Fixing heater temperature failure
Possible cause Step Check Result Remedy
Poor
thermistor
harness
contact 1 Is the contact of connector
CN19 on the main PCB
good? No Reconnect the connector.
Blown thermal
fuse 2 Remove the fixing unit and
measure the resistance of
the thermal fuse. Is it open
circuit? Yes Replace the fixing unit.
Blown
thermostat 3 Remove the fixing unit and
measure the resistance of
the thermostat. Is it open
circuit? Yes Replace the fixing unit.
Halogen
heater lamp
failure 4 Remove the fixing unit and
measure the resistance of
the halogen heater lamp. Is
it open circuit? Yes Replace the halogen heater
lamp.
M-7 Laser Unit failure
Possible cause Step Check Result Remedy
No Reconnect the connector
securely. Harness
connection
failure (1) 1 Is connector CN6 on the
main PCB secured
correctly?
Yes Replace the laser unit.
No Reconnect the connector
securely. Harness
connection
failure (2) 2 Is the connection of the
scanner motor connector
CN6 on the main PCB
secure?
Yes Replace the laser unit.